1. Field of the Invention
The present invention relates to a position detector device for detecting the moving extent, speed and the like of a moving or rotating matter, for example.
2. Description of the Related Art
The conventional position detector device for moving matters will be described with reference to FIGS. 1 through 3.
As shown in FIG. 1, the conventional position detector for moving matters (or rotating matters in this case) includes a magnetic drum 51 provided with a magnetically-recorded section 53 on its side, and a magnetic sensor 52 located to face the magnetic drum 51 and serving to convert changes in magnetic field into electric signals while using magnetic resistance effect. Since the magnetically-recorded section 53 on the side of the magnetic drum 51 is magnetized with a wavelength of .lambda., the intensity and direction of magnetic field entering into the magnetic sensor 52 change as the magnetic drum 51 is rotated. The rotation angle and speed of the magnetic drum 51 can be detected by detecting these changes of magnetic field by means of the magnetic sensor 52.
The magnetic sensor 52 used by this position detector device has such an arrangement as shown in FIG. 2, for example. Magnetic resistance elements A1 and A2 connected in series to each other are connected parallel to magnetic resistance elements B1 and B2 which are also connected in series to each other. Voltage of V is applied from a constant-voltage power source to these magnetic resistance elements. Terminals a and b are connected between the magnetic resistance elements A1 and A2 and between the magnetic resistance elements B1 and B2, respectively, and these four magnetic resistance elements A1, A2, B1 and B2 are arranged at an interval of .lambda./8, as shown in FIG. 3.
When voltage changes between the terminal a and the ground and between the terminal b and the ground are detected while applying voltage of V to between the series-connected magnetic resistance elements and between the other series-connected magnetic resistance elements and keeping the magnetic drum rotating, two-phase signal outputs can be obtained. The two-phase signals thus obtained are false sine waveforms shifted in phase only by a period of 1/4. When these output voltages are converted into pulse waveforms, while detecting the zero cross point of them, and the exclusive "or" of these pulse waveforms is picked up, two pulses can be obtained every time the magnetized pattern on the side of the magnetic drum is rotated one pitch. The rotation angle and speed of the magnetic drum are detected on the basis of this pulse number.
For the purpose of obtaining 2.sup.N (N=1, 2, 3 . . . ) pulses every time the magnetized pattern is rotated one pitch in the case of this conventional position detector device, it is needed that 2(.sup.N+1) pieces of magnetic resistance elements are arranged at an interval of .lambda./2(.sup.N+2). On the other hand, the size of the magnetic sensor becomes larger and the number of terminals needed to connect the magnetic sensor to external circuits also becomes larger as the number of magnetic resistance elements is increased more and more.
The magnetic sensor is usually made according to the vapor-depositing, sputtering or photolithographic process. Its cost can be therefore made lower as the number of magnetic sensors which can be obtained from a wafer becomes larger. As the number of magnetic resistance elements needed becomes larger and the size of the magnetic sensor becomes larger, too, therefore, the cost of the magnetic sensor is naturally made higher. Further, when the number of terminals for the magnetic sensor is thus increased, the number of connecting steps is made larger because of connecting points increased, thereby causing the cost of connecting cables to be added.
It has been strongly desired these days to provide a position detector device, extremely smaller in size and higher in resolution. In the case of the above-described conventional position detector device, however, the size of its magnetic sensor is too large and signals detected by its magnetic sensor are drifted by temperature change.
On the other hand, the diameter of the magnetic drum on the side of which the magnetized pattern is formed can be made smaller to make the position detector device smaller in size, but distances (which will be hereinafter referred to as gap lengths) between the outer circumference of the magnetic drum and some of the magnetic resistance elements of the magnetic sensor become longer. As the result, magnetic intensity applied from the magnetically-recorded section to the magnetic resistance elements cannot be kept certain and output signal waveforms are thus distorted.
Japanese Patent Disclosure Sho 60-196619 discloses a position detector device for measuring the speed of a rotating matter and the passage of a reference position thereof. This position detector device includes a magnetic drum attached to a motor shaft and provided with a magnetically-recorded section on the outer circumference thereof, and a magnetic sensor for converting changes in magnetic field into electric signals while using magnetic resistance effect. The magnetically-recorded section comprises a first and a second encoder tracks. On the first encoder track, a continuous magnetized pattern is recorded. On the second encoder track, plural magnetized patterns are recorded at an interval to create plural reference signals every time the magnetic drum is once rotated. On the other hand, the magnetic sensor includes a magnetic resistance element for detecting magnetic signals from the first encoder track and another magnetic resistance element for detecting reference signal from the second track.
In the case of this position detector device, however, encoder and reference signals must be recorded on the two magnetically-recorded tracks independently of the other and the magnetic sensor must include the magnetic resistance elements one for detecting magnetic signals from the encoder track and the other for detecting those from the reference signal track, so as to obtain encoder and reference signals. The position detector device is therefore unsuitable for being made smaller in size and its material cost is also increased.